For convenience purposes, it is well known to provide garage doors which utilize a motor to provide opening and closing movements of the door. Motors may also be coupled with other types of movable barriers such as gates, windows, retractable overhangs and the like. An operator is employed to control the motor and related functions with respect to the door. The operator receives command signals for the purpose of opening and closing the door from a wireless remote, from a wired wall station or other similar device. It is also known to provide safety devices that are connected to the operator for the purpose of detecting an obstruction so that the operator may then take corrective action with the motor to avoid entrapment of the obstruction.
Safety devices come in many forms for use with a garage door operator. One of the more widely used devices is a photoelectric eye which projects a light beam across the door's travel path. If the light beam is interrupted during closure of the door, the operator stops and/or stops and reverses the travel of the door. This is sometimes referred to as a non-contacting or an external secondary entrapment device. Contact type safety devices such as an edge-sensitive pressure switch, which is attached to the bottom edge of the door and runs the complete width of the door, may also be used. Other contact safety devices directly monitor the operating characteristics of the driving motor to determine whether an obstruction is present. Typically, shaft speed of the motor is monitored by projecting an infrared light through an interrupter wheel. Alternatively, Hall effect switches or tachometers can be used to monitor shaft speed. Or, the motor current could be monitored such that when an excessive amount of current is drawn by the motor—which indicates that the motor is working harder than normal—it is presumed that an obstruction has been encountered. It is also known to monitor door speed with a sliding potentiometer, wherein a rate of change is equated to the speed of the door and wherein unexpected slowing of the door triggers corrective action by the operator. Regardless of how the safety devices work, their purpose is to ensure that individuals, especially children, are not entrapped by a closing door. Opening forces of the door are also monitored to preclude damage to the operating system for instances where an object or individual is caught upon a door panel as the door moves upwardly.
How safety devices are used with a door operator system have evolved from the days of no uniform standard to the currently applied government regulations as embodied in Underwriters Laboratories Standard 325. The standard requires that when an operator is mounted to a pinch-resistant door and an external secondary entrapment device is not connected to the operator, that a fifteen pound obstruction force threshold setting must be used. In other words, if no external secondary entrapment device is attached to the operator then the maximum force that the motor is allowed to apply to the door—in a closing direction—is fifteen pounds. But, if an external secondary entrapment device is attached, then the UL standard does not require a maximum obstruction force setting.
If the end-user selects an operator model without the external secondary entrapment feature, then an input jumper switch is set to disable and the fifteen pound force threshold is used during barrier movement. If the end-user selects an operator model with the external secondary entrapment feature, then the input jumper is permanently enabled and the force threshold value is set at a higher value, typically twenty-five pounds. If the end-user desires to later add the external secondary entrapment feature, then the jumper must be physically moved from a disabled position to an enabled position. If the jumper is not moved to an enabled position then the external secondary entrapment feature will work, but the force threshold remains at fifteen pounds. It has been found that the fifteen pound threshold is quite sensitive and as a result phantom obstructions are encountered. In other words, the operator falsely detects and reacts to a non-existent obstruction in the barrier's path. Such false detections may be the result of the wind, temperature, debris in the door track and the like. These false detections cause the barrier to reverse direction and require the user to wait unnecessarily for the barrier to complete its opening or closing cycle. In any event, there is a need in the art to simplify the later installation of a secondary entrapment feature to an existing operator.